Consumer preferences for personal care compositions such as shampoos and cleansers include fast lathering (“flash lather”) and quick, clean rinsing. Currently available products tend to employ conventional surfactants and co-surfactants, including C10-C18 sulfate blends, which fail to completely meet consumer needs and preferences. For example, lauryl sulfate and lauryl ether sulfate long have been the preferred mainframe surfactants in shampoos and other foaming compositions. Lauryl sulfate provides good lather but may be harsh, causing for example skin and eye irritation, and further may precipitate on dilution leaving surfactant residues as water hardness increases. Lauryl ether sulfate may mitigate harshness and improve hardness sensitivity, but at typical ethoxylation levels, i.e. (OCH2CH2)3, or EO3, is a poor latherer and relatively weight inefficient.
There exists a need, therefore, to identify combinations of surfactants and co-surfactants which result in products having flash lather and quick rinsing characteristics, which are not harsh on the skin and are relatively hardness insensitive, and are suitable for use in consumer products.
The present invention meets the aforementioned needs. Applicants unexpectedly have found that compositions comprising undecyl (C11) sulfates and undecyl ethoxysulfates (“undeceth sulfates”) with low ethoxylation (“EO content”) (e.g. singly ethoxylated) have many of the characteristics necessary to fulfill consumer needs and preferences in personal care products. Though previously taught as a member of the group of C10-C18 sulfate surfactants, the undecyl sulfates were thought to be less suitable for personal care compositions based on studies of lather and foaming properties that were conducted using relatively dilute concentrations (less than 1000 ppm). For example, U.S. Pat. No. 4,732,707 advises that compositions should not contain more than 1% C11. Applicants have found, however, that at higher concentrations (for example 3,000 ppm and above), undecyl sulfate and the single ethoxylate of undecyl sulfate (undecyl EO1 sulfate) exhibit properties such as low surface tension and higher critical micelle concentration (CMC). It is believed that these properties contribute to compositions having fast lathering and quick rinsing which is superior to either dodecyl sulfates or lauryl sulfates (C12-C16 blends, e.g., typically having a ratio of 68/27/5 C12/C14/C16), and which are mild and relatively insensitive to water hardness. Such compositions are suitable for use in shampoos, personal cleansers, and other personal care compositions, and may be used in combination with other surfactants, structured surfactants, beauty benefit agents (e.g., conditioner), co-surfactants and/or rheology modifiers to provide desirable consumer benefits.